The vast majority of world-wide prime mover capacity is in the form of internal combustion engines. These include engines in automobiles, trucks, tractors, ships, airplanes, and stationary plants. Thermodynamically, engines are classified according to their basic cycle.
A volumetric internal combustion engine possesses an advantage over a conventional gas turbine engine in that it operates by means of static pressure within a closed volume which enables effective and efficient operation with low dependence on engine velocity and therefore relatively high efficiency and output through a wide range of engine velocity. Also its parts can generally work at temperatures much less than the maximum cyclic temperature. As a result, said maximum cyclic temperature may be high, thereby allowing for a high cyclic efficiency. Other advantages associated with the volumetric internal combustion engine include its relatively low cost, high mechanical efficiency and wide variation in speed and load. These advantages are of particular importance in the field of land transportation.
A typical single-shaft open-type gas turbine engine designated by numeral 10 is illustrated in FIG. 1. Gas turbine engine 10 comprises compressor 2, combustor 6 and turbine 7, which is coupled to the compressor by shaft 8. Atmospheric air 3 enters compressor 2, in which its pressure and temperature is increased. The compressed air is then forced into combustor 5, in which it mixes and burns with a fuel. Hot pressurized combustion gases 9 expand within turbine 7 and achieve a higher velocity, causing shaft 8 to rotate, thereby driving compressor 2 and any load connected to the shaft, due to the kinetic energy of the combustion gas stream. Combustion gases 9 are then discharged to the atmosphere. The net work of the cycle is the difference between the work obtainable in the expansion process and the work of compression.
Relative to a volumetric engine, a gas turbine engine has a greater power to weight ratio, and therefore its size is smaller than its volumetric engine counterpart at a given power output. A gas turbine engine is capable of rapid start-up and loading, and is likely to have a long life. Also, an open-type gas turbine engine offers the advantage of simple sealing systems. No effective cooling is possible.
A gas turbine engine has good efficiency at full load when the operation temperature and kinetic energy of the combustion gases, compressor pressure ratio, and rotational velocity of the shaft are high. However, the efficiency is reduced when the load is lowered, such as by lowering the operation temperature or the rotational velocity of the shaft. Consequently, prior art gas turbine engines have been usually found to be suitable for those applications requiring substantially constant rotational velocity and output, such as transcontinental aircraft or power plants, but heretofore have been found not to be suitable for uses such as land transportation or light aircraft, which require wide variations in speed and load.
As previously mentioned, the performance of a gas turbine engine is directly related to the temperature of the combustion gases. Various types of combustors in which combustion is completed have been employed to maximize the temperature of the combustion gases, while the temperature that turbine components can withstand is generally the limiting factor concerning the upper limit of the combustion gas temperature. The complexity and cost of combustors has therefore increased, particularly due to the need to provide relatively cool air such that it is mixed with the hotter flame and/or combustion gases produced within the corresponding combustor, for preventing damage to the associated turbine components. The mixing process ends needs to be completed prior to the introduction into the turbine. A gas turbine engine system which employs a less complex combustor would therefore be desirable.
It is an object of the present invention to provide a combustion engine system, particularly a gas turbine engine, that allows for a wide variation in speed and load.
It is an additional object of the present invention to provide a gas turbine engine that is suitable for use in land transportation.
It is an additional advantage of the present invention to provide a combustion engine system that can efficiently burn a broad range of fuels.
It is another object of the present invention to provide a combustion engine system that is cost effective.
It is a further object of the present invention to provide a gas turbine engine that overcomes the disadvantages of the prior art devices while retaining their inherent advantages.
It is a still further object of the present invention to combine the advantages of volumetric systems with those of flow systems.
It is yet an additional object of the present invention to provide an engine system by which combustion may be completed externally to the combustors, thereby reducing combustor complexity.
Other objects and advantages of the invention will become apparent as the description proceeds.